As interior materials, resin felts comprising a phenol-aldehyde condensation resin with fibers charged thereto, foamed article of synthetic resins, polypropylene composites, cardboard of polypropylene, and the like which are resistant against temperatures of 100.degree. C. or more have been used. Of those materials, the resin felt is excellent in stiffness, shape-holding properties after heat circulation (thermal resistance), and dimensional stability, but has disadvantages in that moldability, impact resistance, air permeability and lightness are poor. The cardboard or polypropylene is excellent in stiffness and lightness, but is inferior in air permeability. Moreover, since a corrugate material is used, the strength is critical in direction. The foamed article of synthetic resin such as cross-linked polystyrene is excellent in lightness, but has disadvantages in that shape-holding stability after heat circulation and bending properties are poor. Material satisfying all the requirements as an interior material, such as stiffness, proper flexibility, lightness, dimensional stability, shape-holding properties after heat circulation (thermal resistance), and moldability has not been obtained.
A method for producing non-woven fabrics having good elasticity comprising temporarily fixing fibers of the top and bottom layers of web by needling a fiber mat of synthetic fibers with fibers of polyethylene, polypropylene, polyester having a low melting point (e.g., 140.degree. C.) and the like as a fiber binder, and melting the above fiber binder by heating to thereby bind the other synthetic fibers is known. This non-woven fabric is good in lightness and flexibility, but is inferior in moldability and stiffness. Therefore, such non-woven fabric is useful as an interior material which is used in a flat place, but is not useful as an interior material which is used in a complicated place.
An interior material for automobile produced by impregnating or coating a needle punch cloth with an aqueous emulsion of a thermoplastic resin having a softening point of 100 to 130.degree. C., heating and drying the cloth to remove water and obtain a moldable non-woven fabric, and then further heating and press molding (compression molding) the fabric is known. This interior material has an advantage in that it can be used in a place of complicated form. Mechanical bond of fibers of the non-woven fabrics is conducted by intertwining the fibers each other and attaching the emulsion resin to the fibers. However, since the apparent density of the non-woven fabrics which are coated or impregnated with the emulsion resin is as high as 0.08 to 0.13 g/cm.sup.3, the effect of filling spaces between fibers with the emulsion resin is poor.
As a process for producing non-woven fabrics which are improved in the inherent disadvantages of dimensional stability and stiffness of the moldable nonwoven fabric without reducing the lightness, shape-holding properties after heat circulation, and air permeability, the present inventors have proposed a process in which a fiber mat comprising 15 to 50 wt% of a thermoplastic resin binder fibers and 85 to 50 wt% of synthetic fibers or natural fibers having a melting point of more than 40.degree. C. higher than that of the thermoplastic resin is needled, the mat is heated at a temperature at which the thermoplastic resin binder fibers are melted but the synthetic or natural fibers are not melted, the fiber mat is pressed while the thermoplastic resin binder fibers maintain a molten state, to thereby adjust the apparent density of the mat to 0.15 to 0.50 g/cm.sup.3, the pressed mat is coated or impregnated with an aqueous emulsion of a thermoplastic resin having a moldable temperature range of 80 to 180.degree. C. in such an amount that the resin content of the emulsion is 15 to 300 wt% based on the weight of the fibers in the fiber mat, and then the mat is heated to 60 to 250.degree. C. and dried to remove water and obtain the desired non-woven fabrics as disclosed, for example, in Japanese Patent Application (OPI) No. 87353/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
This method has a great feature in that the stiffness of the non-woven fabrics is increased by using the fiber binder made of a thermoplastic resin in combination with the resin emulsion, the dimensional stability is increased by bonding the fibers each other, and the stiffness of the non-woven fabrics is increased by removing a part of air by compressing the fiber mat before coating or impregnating with the emulsion resin to thereby increase the filling efficiency of the emulsion resin into the mat (i.e., the amount of the emulsion resin which fills spaces between fibers of web).
This process for producing moldable non-woven fabrics requires a preceding heating step to melt the binder fibers and a subsequent heating step to dry the resin emulsion, and this is disadvantageous from a standpoint of heat energy.